Robot-assisted sheet metal bending loading and unloading path planning method based on svsdf

A robot-assisted sheet metal bending loading and unloading path planning method based on a Swept Volume Signed Distance Field (SVSDF), comprising the following steps:

• Step 1, constructing a two-dimensional pixel coordinate system, wherein a two-dimensional map plane is constructed after binarizing side-view images of three-dimensional models of upper and lower dies based on a sheet metal bender, an upper left corner of the two-dimensional map plane is used as an origin, and two adjacent right-angled edges passing through the origin are an x axis and a y axis, respectively, so that the two-dimensional pixel coordinate system is formed;
• if the sheet metal part is regarded as a moving object, and a bending point of the sheet metal part is regarded as a moving point, a motion path of loading and unloading the sheet metal part comprises several path points, and each path point is denoted as (x, y, θ);
• wherein (x, y) is a position parameter of the sheet metal part in the two-dimensional pixel coordinate system;
• and θ is an attitude angle of the sheet metal part;
• Step 2, obtaining an initial motion trajectory of loading and unloading the sheet metal part, wherein a Rapidly-Exploring Random Tree (RRT)-Connect algorithm is used to initially plan the motion path of loading and unloading the sheet metal part to obtain an initial motion trajectory of loading and unloading the sheet metal part;
• and the initially planning process is repeated for Npop times to obtain Npop initial motion trajectories of loading and unloading the sheet metal part;
• Step 3, calculating path safety, wherein all pixel points which are prone to colliding with bending motion of the sheet metal part or have a distance less than a safe distance from an upper die and a lower die of the sheet metal bender are found, which are marked as obstacle points of interest;
• and according to the obstacle points of interest and the initial motion trajectory of loading and unloading the sheet metal part, and based on the SVSDF, the path safety value of each initial motion trajectory of loading and unloading the sheet metal part is calculated;
• Step 4, calculating path cost, wherein assuming that any initial motion trajectory of loading and unloading the sheet metal part has N path points, the specific calculation formula of the path cost is:
• path
• ⁢
• cost
• =
• ∑
• i
• =
• 1
• N
• -
• 1
• Δ
• ⁢
• x
• i
• 2
• +
• Δ
• ⁢
• y
• i
• 2
• +
• β
• ⁢
• Δ
• ⁢
• θ
• i
• 2
• wherein Δxi and Δyi are differences in horizontal and vertical position parameters between two adjacent path points i and i+1;
• 1≤i≤N−1;
• Δθi is a difference in attitude angles of the sheet metal part between two adjacent path points i and i+1;
• β is an attitude angle weight coefficient, which is a set value;
• Step 5, calculating COSTt, wherein a fitness value COSTt of a t-th initial motion trajectory of loading and unloading the sheet metal part is calculated, 1≤t≤Npop;
• and the calculation formula of COSTt is:
• COST
• t
• =
• γ
• 1
• ⁢
• path
• ⁢
• cost
• +
• γ
• 2
• ⁢
• path
• ⁢
• safety
• wherein γ1 is a cost weight coefficient, and 1≤γ1≤1.5, which is a set value;
• γ2 is a safety weight coefficient, and 1≤γ2≤1.5, which is a set value;
• and
• Step 6, obtaining an optimal motion trajectory of loading and unloading the sheet metal part, wherein based on a Water Cycle Algorithm (WCA), the minimum value of Npop COSTt in Step 5 is continuously iteratively optimized and found out, and the motion trajectory of loading and unloading the sheet metal part corresponding to the minimum COSTt is used as the optimal motion trajectory of loading and unloading the sheet metal part.